NSM defaultVR and management VR

When trying to manage juniper ISG2000 and SSG550 under screenOS 6.2.0r9we can select default VR and/or management VR on the NSM window..When we select a VR as management VR , it automatically changes the valueof default VR to the onr choosen as management VR on the NSM screen and vice versa..Is this behavior normal ?It is an NSM bug ?